Low pressure lift bags have long been used for emergency rescue operations where heavy objects are required to be lifted. For the purposes of this application, it will be understood that the term "heavy" is used qualitatively to identify objects such as vehicles and the like which cannot be lifted easily by hand, rather than quantitatively. Typically, these lift bags are initially maintained in a relatively flat state so that they may be readily positioned under the object to be lifted. Once the flat lift bag is placed beneath the object to be lifted, air pressure may be dispensed from an air hose or the like to the lift bag through an inflation tube extending from the bag, thereby inflating the bag to heights of typically about 24 inches to 48 inches. Because of their relatively low air pressure (previously about 7 to 7.5 psig) and their relatively large surface area, many low pressure lift bags are seen as being effective for lifting heavy objects to significantly large heights relatively easily and safely. In contrast, high pressure bags, i.e., those suited to operate at about 118 psig or more, are known to lift heavier loads than the low pressure bags, but typically are only capable of lifting loads to significantly shorter heights.
Nevertheless, these single-chambered, low pressure lift bags are not suitable for all lifting purposes. For instance, when the bag is being inflated, air will go to the area of least resistance before it begins to lift the heavy object. In many cases, this will cause the bag to roll or twist under the load, and may even cause the load itself to shift. Consequently, when this happens, the operator has to stop the lift, deflate the bag, and reposition the bag before inflating it again. Furthermore, because the air in the bag will go to the area of least resistance, the bag will first inflate outwardly with its side walls ballooning before the bag will do any lifting. Again, this could cause the load being lifted to shift and may cause the bag to work like a spreader rather than a jack. Because the side walls of the bag must become fully inflated prior to lifting the load, the victim must be watched and protected from being pushed or crowded by the bag as it is inflated.
Another major problem with low pressure lift bags is the inconvenience associated with deflating the bags. Because most low pressure bags have side walls, they must be constantly manipulated by pushing and folding the sides inward in order to have the bag situated for its next use. In fact, it is essentially impossible to get the bag to deflate to its original position without the user struggling to fold the side walls inward.
Yet another problem pertains to the fabrication of the bags. Currently, there are at least two types of low pressure lift bags available to the emergency rescue industry. Both of these types of bags are single chambered bags constructed of a fabric such as nylon, canvas or other synthetic fibrous fabric such Kevlar.TM. coated with rubber such as neoprene. To make the conventional lift bags, the coated fabrics are cut into various sizes to form a pattern and cold glued to secure the side walls and various other parts of the bag together. To make certain areas of the bag stronger and stiffer, the manufacturer typically glues more than one layer of fabric together to form certain parts of the bag such as the top surface and bottom surface. This method of fabrication, known as the "cut and paste" operation, is generally well known in the art.
However, a major problem with this technology is that the glue has been shown to crystallize and fail after about 10 to 12 years of use, even when stored in controlled storage environments. Consequently, the life of the fabric (providing it is not torn or ruptured) far outlasts the life of the glue. Moreover, the use of glue limits the amount of air pressure used in the bags. Typically, bags using current glue technology achieve burst pressures of only about 15 to 20 psig. That is, while most of these air bags are only operatively filled to a pressure of only about 7 to 7.5 psig, the burst pressures (not operating pressures) of these bags have been found to be typically about 1.5 times the operating pressure, although a few of these bags have been known to have slightly higher burst pressures of up to about 2.5 times the operating pressure, i.e., about 15 to 20 psig, when unrestrained by an object to be lifted. It has been found that operating these low pressure lift bags at higher inflation pressures may rupture the bag during lifting or will not permit the lifting of the heavy object to be adequately controlled and stabilized.
In addition, even though the strength and toughness of the fabric used in these bags have improved over the years, only certain gauges of fabric are suitable for this type of "cut and paste" operation used to fabricate the bags. According, it is still possible to puncture and cut the thin fabric. Moreover, the rubber coating on the fabric has been known to peel off due simply to abrasion and normal wear.
With respect to the two types of lift bags currently available, one type comprises a single chamber and generally includes upper and lower surfaces and expandable side walls folded within the deflated bag. As noted hereinabove, when inflated, this type of lift bag typically expands outwardly and vertically, such that the side walls unfold and expand between the upper and lower surfaces. The resultant inflated lift bag expands to the point where it appears to be a bulging box, relatively cubical in shape. The shape of the bag is generally dictated by the number of layers of fabric used to form the top and bottom surfaces. The stiffness of these areas allows the bag to hold its shape as well as offers protection from the item being lifted and the ground. Of course, when restrained between a flat object parallel to the floor and the floor itself, an area on the top surface of the bag contacting the object to be lifted and an area on the bottom surface of the bag communicating with the floor or like surface will lie generally flat against the object and floor, rather than bulge as noted when inflated and unrestrained.
This type of bag may also be employed as a medium pressure air bag, i.e., it may have an air pressure of about 14.7 psig, provided the rubber-coated fabric and glue are sufficient. However, these lift bags are not adjustable so that they cannot be used at low pressures as well. In other words, these bags are to be used at either low pressure (about 7-7.5 psig) or medium pressure (about 14-15 psig).
The second type of low pressure lift bag known in the art is similar to the above-described lift bag except that it is cylindrical in shape. Notably, it also has only one inflation chamber and includes upper and lower surfaces and side walls which are folded to flatten the bag when in the uninflated condition. Again, as noted hereinabove, upon inflation, the top of the bag expands vertically only after the side walls unfold and expand upwardly and outwardly, such that the bag forms a generally bulging cylinder or other shape depending on the design of the top and bottom surfaces. Furthermore, as noted hereinabove, an area on the top surface of the bag contacting a flat object to be lifted and an area on the bottom surface of the bag communicating with the floor or similar stationary surface will lie generally flat against the object and the floor when in proper use.
However, one major problem which this type of bag is its ability to "kick" out from under the load while the load is being lifted but before the bag is fully inflated. This typically happens when performing lifts which must be lifted to a relatively high height, usually about 36 inches or so and when the bag is not properly positioned under the load. This occurs because, when the bag is not positioned directly under the load, the load travels along an arcuate path as it is being lifted from the ground to a considerable height. Because the top and bottom surfaces generally try to stay flat to the ground, the side walls bend to accommodate the arcuate path, thereby causing the bag to twist and "kick" out from under the load. Moreover, this bag is very susceptible to falling over or rolling over while being inflated.
To stabilize the bag somewhat, some manufacturers use internal straps to try to keep the top and bottom surfaces of the bag parallel to each other. However, as detailed hereinabove, if the top and bottom are not properly aligned, the bag will "walk" or roll over onto its side where there is less protection from possible ruptures due to the thinness of the bag at its side walls. Even with the internal straps, there is no guarantee that the bag will not roll over.
In addition, the conventional lift bags may include an upper gripping surface which is typically glued to the top of the bag. However, this gripping surface does not provide an effective means to keep the heavy object being lifted by the bag from sliding or otherwise moving during the lifting process inasmuch as it is not provided with a suitably rough or friction-providing gripping pad having that specific capability.
Furthermore, the air inlets on these types of bags are not repairable. Consequently, should the inlet be cut, pulled off or otherwise damaged in any way, the bag, in most cases, will be unusable. For these conventional lift bags the air inlet is simply a rubber tube made from the same rubber-coated fabric as the rest of the bag. The tube is usually glued inside the bag and may include a sleeve glued over the outside area of the tube. The inlet tube generally extends from the bag about 4 to 6 inches. Typically, a metal claw fitting or coupling is clamped or crimped to the end of the rubber tube. Notably, however, the weight of the metal fitting may cause the end of the tube to sag, thereby causing the tube to flex. After several years, it has been found that this flexing and wearing of the tube begins to cause the rubber coating to wear off, thereby causing the tube to leak.
Still further, the conventional lift bags do not provide a relief valve to allow any overabundance of air to escape. Thus, any overinflating of the lift bags may cause them to rupture.
Finally, these conventional lift bags have tethering straps which are simply glued to tethering points on the lift bags. There is no reinforcement at these tethering points and thus, if the load were to shift during lifting with the tethering straps already tied as appropriate, the straps could pull out of the bag, thereby possibly damaging the bag.
Therefore, the need exists for a lift bag having multiple inflation chambers to provide improved stability and greater flexibility over existing single-chambered lift bags. The need also exists for a lift bag which can be operated at pressures up to about 15 psig for specified heights and which include inflation and relief valves for each of the chambers of the lift bag.